Method of fabricating nitride-based compound layer, GaN Substrate and vertical structure nitride-based semiconductor light emitting device

ABSTRACT

In a method for fabricating a nitride-based compound layer, first, a GaN substrate is prepared. A mask layer with a predetermined pattern is formed on the GaN substrate to expose a partial area of the GaN substrate. Then a buffer layer is formed on the partially exposed GaN substrate. The buffer layer is made of a material having a 10% or less lattice mismatch with GaN. Thereafter, the nitride-based compound is grown laterally from a top surface of the buffer layer toward a top surface of the mask layer and the nitride-based compound layer is vertically grown to a predetermined thickness. Also, the mask layer and the buffer layer are removed via wet-etching to separate the nitride-based compound layer from the GaN substrate.

CLAIM OF PRIORITY

This application claims the benefit of Korean Patent Application No.2005-53331 filed on Jun. 21, 2005 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating anitride-based compound layer, a GaN substrate and a verticalnitride-based semiconductor light emitting device. More particularly,the present invention relates to a method for fabricating anitride-based compound layer, a GaN substrate and a verticalnitride-based semiconductor light emitting device capable of recyclingthe expensive GaN substrate by forming a mask layer with a predeterminedpattern and a buffer layer on the GaN substrate, laterally growing thenitride-based compound layer, and removing the mask layer and the bufferlayer via wet-etching to separate the GaN substrate without impairment.

2. Description of the Related Art

In general, a nitride-based compound is a group III-V compound crystalsuch as GaN, InN, and AlN, which is widely used for a light emittingdevice generating light of a short wavelength (ultraviolet ray and greenlight), especially blue light. The nitride-based compound has beentypically manufactured via a sapphire substrate or a SiC substrate dueto absence of a commercially available substrate that satisfies latticematch conditions for crystal growth. But the sapphire substrate or SiCsubstrate has lattice mismatch with the nitride-based compound. Thisrenders it very difficult to grow a high-quality nitride-based compoundon the sapphire or SiC substrate.

Meanwhile, a substrate having lattice match with the nitride-basedcompound, such as a GaN substrate, has been fabricated. However, the GaNsubstrate is very expensive, and unrecyclable owing to grinding andabrasion that occur during lapping and polishing in a manufacturingprocess of the light emitting device.

FIG. 1 is a cross-sectional view partially illustrating a method forfabricating a nitride-based light emitting device using a GaN substrateaccording to the prior art. As shown in FIG. 1(a), in a conventionalmethod, a light emitting structure 12 made of a nitride-based compoundsemiconductor is formed on a GaN substrate 11 with a predeterminedthickness d. Then in order to easily separate a final structure obtainedinto individual devices, an underside of the GaN substrate is ground andabraded via lapping and polishing to reduce the thickness d′ of the GaNsubstrate 11 as shown in FIG. 1(b).

This conventional method for fabricating the nitride-based semiconductorlight emitting device using the GaN substrate is disadvantageous in thatthe high-priced GaN substrate is unrecyclable due to grinding andabrasion caused by lapping and polishing.

Therefore, in the art, there has been a demand for a technology ofrecycling the high-priced GaN substrate to reduce production costs.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an object according to an aspect of thepresent invention is to provide a method for fabricating a nitride-basedcompound layer, a GaN substrate and a vertical nitride-basedsemiconductor light emitting device capable of recycling the expensiveGaN substrate by forming a mask layer with a predetermined pattern and abuffer layer on the GaN substrate, laterally growing the nitride-basedcompound layer, and removing the mask layer and the buffer layer viawet-etching to separate the GaN substrate without damage.

According to an aspect of the invention for realizing the object, thereis provided a method for fabricating a nitride-based compound layer,comprising steps of:

preparing a GaN substrate;

forming a mask layer with a predetermined pattern on the GaN substrateto expose a partial area of the GaN substrate;

forming a buffer layer on the partially exposed GaN substrate, thebuffer layer made of a material having a 10% or less lattice mismatchwith GaN;

laterally growing a nitride-based compound from a top surface of thebuffer layer toward a top surface of the mask layer and verticallygrowing the nitride-based compound layer to a predetermined thickness;and

removing the mask layer and the buffer layer via wet-etching to separatethe nitride-based compound layer from the GaN substrate.

Preferably, the buffer layer has a 5% or less lattice mismatch with GaN.

According to an embodiment of the invention, preferably, the bufferlayer comprises one selected from a group consisting of ZnO, Ga₂O₃ andZrB₂. Preferably, the mask layer comprises a silicon oxide film or asilicon nitride film. Also, preferably, a wet-etching solution used inthe wet-etching comprises HCl.

According to another aspect of the invention for realizing the object,there is provided a method for fabricating a GaN substrate comprisingsteps of:

preparing a seed GaN substrate;

forming a mask layer with a predetermined pattern on the seed GaNsubstrate to expose a partial area of the GaN substrate;

forming a buffer layer on the partially exposed seed GaN substrate, thebuffer layer made of a material having a 10 % or less lattice mismatchwith GaN;

laterally growing the GaN from a top surface of the buffer layer towarda top surface of the mask layer and vertically growing the GaN to formthe GaN substrate with a predetermined thickness; and

removing the mask layer and the buffer layer via wet-etching to separatethe GaN substrate from the seed GaN substrate.

According to another embodiment of the invention, preferably, the GaNsubstrate forming step comprises growing the GaN by HVPE.

According to further another aspect of the invention for realizing theobject, there is provided a method for fabricating a vertical nitridesemiconductor light emitting device, comprising steps of:

preparing a GaN substrate;

forming a mask layer with a predetermined pattern to expose a partialarea of the GaN substrate;

forming a buffer layer on the partially exposed GaN substrate, thebuffer layer made of a material having a 10% or less lattice mismatchwith GaN;

laterally growing a first conductivity-type nitride-based compoundsemiconductor doped with first conductive impurities from a top surfaceof the buffer layer toward a top surface of the mask layer andvertically growing the first conductivity-type nitride-based compoundsemiconductor to form a first conductivity-type nitride-based compoundsemiconductor layer, and growing an active layer made of a nitride-basedcompound on the first conductivity-type nitride-based compoundsemiconductor layer and a second conductivity type nitride-basedcompound layer doped with second conductive impurities on the activelayer, thereby forming a light emitting structure.

forming a conductive carrier substrate on the light emitting structure;and

removing the mask layer and the buffer layer via wet-etching to separatethe light emitting structure from the GaN substrate.

According to further another embodiment of the invention, preferably,the light emitting structure forming step comprises growing thenitride-based semiconductor compound by MOCVDE.

According to further another embodiment of the invention, the method forfabricating the vertical nitride semiconductor light emitting devicefurther comprises forming a first electrode on an underside of the firstconductivity-type nitride-based compound semiconductor layer from whichthe GaN substrate is separated, and a second electrode on a top surfaceof the conductive carrier substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view illustrating a method for manufacturinga nitride-based semiconductor light emitting device via a GaN substrateaccording to the prior art;

FIG. 2 is a cross-sectional view illustrating a method for manufacturinga nitride-based semiconductor light emitting device and a GaN substrateaccording to an embodiment of the invention;

FIG. 3 is a schematic view illustrating defects in a nitride-basedsemiconductor layer grown laterally; and

FIG. 4 is a cross-sectional view illustrating a method for manufacturinga vertical nitride-based semiconductor light emitting device accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention, however, be embodied in maydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the shapes and dimensions may be exaggerated for clarity, andthe same reference signals are used to designate the same or similarcomponents throughout.

FIG. 2 is a cross-sectional view illustrating a method for fabricating anitride-based compound layer and a GaN substrate according to anembodiment of the invention. In FIG. 2, reference numeral 24 denotesboth a nitride-based compound layer and a GaN substrate fabricated.Unless explained otherwise, the term “nitride compound layer” isconstrued to include the GaN substrate. In addition, when it isnecessary to distinguish the GaN substrate for growing the nitride-basedcompound layer from the GaN substrate fabricated, the GaN substrate forgrowing the nitride-based compound layer is termed a “seed GaNsubstrate”.

Referring to FIG. 2, first, as shown in FIG. 2(a), a GaN substrate 21 isprepared and a mask layer 22 with a predetermined pattern is formed onthe GaN substrate 21. The mask layer 22 is made of a material removableby a later wet-etching process. The material for the mask layer 22 isexemplified by dielectrics such as a silicon oxide film or a siliconnitride film, and the silicon oxide film is most preferable. The masklayer 22 can be formed by depositing the dielectrics via Plasma ChemicalVapor Deposition (PCVD). Preferably, the mask layer 22 is formed of aplurality of stripes which are uniformly spaced and disposed parallel toone another, and a top surface of the GaN substrate 21 is exposedtherebetween.

Then, as shown in FIG. 2(b), a buffer layer 23 made of a material havinga 10% or less lattice mismatch with GaN is formed on the exposed GaNsubstrate 21. The lattice mismatch with the GaN can be calculatedthrough Equation 1 below: $\begin{matrix}{{{\Delta\quad a} = {{\frac{a_{\chi} - a_{GaN}}{a_{Gan}}} \times 100}},} & {{Equation}\quad 1}\end{matrix}$

where Δa is a difference in lattice mismatch with GaN (%), a_(x) is alattice constant of a comparative material, and a_(GaN) is a latticeconstant of GaN.

The buffer layer 23 is made of a material having preferably a 10%lattice mismatch with GaN, and most preferably a 5 % or less latticemismatch. In case where the nitride-based compound layer is grown from atop surface of the buffer layer in a later process, crystal informationof the underlying GaN substrate 21 is transferred through the bufferlayer 23. Thus a smaller difference in lattice constant between thebuffer layer 23 and the GaN leads to a higher-quality nitride-basedcompound layer. For example, when Equation 1 is employed, ZnO with alattice constant of 3.325 Å has a lattice constant difference of about4% from the GaN with a lattice constant of 3.184 Å. The buffer layer 23should exhibit the aforesaid crystal characteristics and be made of amaterial easily removable together with the mask layer 22 in a laterwet-etching process. The material satisfying such properties isexemplified by the aforesaid ZnO, Ga₂O₃ or ZrB₂. The buffer layer 23 maybe formed of the aforesaid material via sputtering or Chemical VaporDeposition (CVD).

Next, as shown in FIG. 2(c), a nitride-based compound 24 is laterallygrown from the top surface of the buffer layer 23 toward a top surfaceof the mask layer 22. Preferably, the nitride-based compound has acomposition expressed by Al_(x)In_(y)Ga_((1-x-y))N, where 0≦x≦1 0≦y≦1and 0≦x+y≦1. To fabricate a GaN substrate, the GaN is employed for thenitride-based compound. After the lateral growth process, thenitride-based compound is vertically grown into the nitride-basedcompound layer having a predetermined thickness as shown in FIG. 2(d).In this process, the nitride-based compound is grown by a well-knowndeposition process such as Metal Organic Chemical Vapor Deposition(MOCVD), Molecular Beam Epitaxy (MBE) or Hydride Vapor Phase Epitaxy(HVPE). Especially, in a process for growing the GaN substrate,preferably, the HVPE is adopted. Such lateral growth and vertical growthcan be achieved by adjusting several conditions for a depositionprocess. For example, a higher temperature and a lower pressure in thedeposition, and a higher ratio of group III-V materials (V/III) enhancesthe lateral growth

The aforesaid lateral growth is suited to grow a high-qualitynitride-based semiconductor layer. FIG. 3 is a schematic viewillustrating defects in the nitride-based semiconductor layer formed bylateral growth. A seed GaN substrate exhibits less defect (dislocation)density, but defects are transferred to the overlying nitride-basedcompound layer grown epitaxially. Therefore, by a general growth method,it is hard to fabricate the nitride-based semiconductor layer having ahigher quality than the seed GaN substrate. But as shown in FIG. 3, bythe lateral growth, some defects d1 of the seed GaN substrate 21 areblocked from being transferred to the nitride-based compound layer 24 bythe mask layer 23. This allows the nitride-based compound layer 24 tohave a higher quality and lower defect density than the seed GaNsubstrate 21.

Then, referring to FIG. 2(d), after the nitride-based compound layer 24is grown, the mask layer 22 and the buffer layer 22 are removed viawet-etching. A wet-etching solution used in the wet-etching of the masklayer 22 and the buffer layer 23 is exemplified by HCl or HCl. Thiswet-etching process removes the mask layer 22 and the buffer layer 23,thereby separating the newly grown nitride-based compound layer 24 fromthe seed GaN substrate, as shown in FIG. 2(e).

The removal by the wet-etching does not affect the high-priced seed GaNsubstrate 21, which thus becomes recyclable. Also, the lateral growthproduces the nitride-based compound layer or GaN substrate having a highquality than the seed GaN substrate 21.

According to the invention, a vertical nitride-based semiconductor lightemitting device is fabricated by employing the aforesaid method forforming the nitride-based compound layer. FIG. 4 is a cross-sectionalview illustrating a method for fabricating a vertical nitride-basedsemiconductor light emitting device according to the invention.

First, referring to FIG. 4(a), a light emitting structure 31 is formedby the aforesaid method for growing the nitride-based compound layer.The light emitting structure 31 includes a first conductivity typenitride-based compound semiconductor layer 31 a, an active layer 31 bformed on the first conductivity type nitride-based compoundsemiconductor layer 31 a and a second conductivity-type nitride-basedcompound semiconductor layer 31 c formed on the active layer 31 b. Toform the first conductivity-type nitride-based compound semiconductorlayer 13 a, a first conductivity-type nitride-based compoundsemiconductor doped with first conductive impurities are laterally grownfrom a top surface of the buffer layer 23 formed on the GaN substrate 21toward a top surface of the mask layer 22. Then the first conductivitytype nitride-based compound semiconductor is vertically grown. Also, theactive layer 31 b is made of the nitride-based compound semiconductorand the second conductivity-type nitride-based compound semiconductorlayer 31 c is doped with second conductive impurities.

In the method for manufacturing the nitride-based semiconductor lightemitting device according to the invention, the mask layer 22 and thebuffer layer 23 are formed in a manner equal to the aforesaid method forforming the nitride-based compound layer. The only difference is that inlaterally growing the first nitride-based compound semiconductor, thefirst conductive impurities are doped to fabricate a conductivesemiconductor. For example, if the first conductivity type is n-type,Si, Ge, Se, Te or C may be added for the first conductivity typeimpurities. The active layer 31 b, which serves to emit light, has asingle or multiple quantum well structure and is made of thenitride-based compound such as GaN or InGaN. Also, if the secondconductivity type is p-type, the second conductivity type nitride-basedcompound semiconductor layer 31 c is doped with p-type impurities suchas Mg, Zn or Be. The light emitting structure can be formed via awell-known deposition process such as MOCVD, MBE or HVPE, and the MOCVDis most preferable.

Next, as shown in FIG. 4(b), a carrier substrate 32 is formed on thesecond conductivity-type nitride-based compound semiconductor layer 31c. The conductive carrier substrate 32 is made of Si, GaAs or aconductive metal. The conductive carrier substrate 32 is bonded to thesecond conductivity-type nitride-based compound semiconductor layer 31 cvia an additional intermediate layer. Alternatively, to form theconductive carrier substrate 32, a metal plating layer may be formed onthe second conductivity type nitride-based compound semiconductor layer31 c to a predetermined thickness. In the vertical nitride-basedsemiconductor light emitting device according to the invention, lightexits through a surface of the first conductivity-type nitride-basedcompound semiconductor layer 31 a from which the GaN substrate 21 isseparated. Therefore, a reflective layer maybe formed between the secondconductivity type nitride-based compound semiconductor layer 31 c andthe conductive carrier substrate 32.

Then, as shown in FIG. 4(c), after the conductive carrier substrate 32is formed, the mask layer 22 and the buffer layer 23 are removed viawet-etching to separate the light emitting structure 31 from the GaNsubstrate 21. As described above, according to the invention, theexpensive GaN substrate 21 is separated unharmed via wet-etching, andthus recyclable.

Thereafter, as shown in FIG. 4(d), a first electrode 33 is formed on anunderside of the first conductivity type nitride-based compoundsemiconductor layer 31 a from which the GaN substrate is separated, anda second electrode 34 is formed on a top surface of the conductivecarrier substrate 32. Then, as shown in FIG. 4(e), a final structureobtained is divided into individual devices, thereby completing thevertical nitride-based semiconductor device. In the verticalnitride-based semiconductor light emitting device, light chiefly exitsthrough the underside surface of the first conductivity typenitride-based compound semiconductor layer 31 a from which the GaNsubstrate is separated. To improve current spread, a transparentelectrode layer made of ITO may be interposed between the firstelectrode 33 formed on the underside of the first conductivity typenitride-based compound semiconductor layer 31 a and the firstconductivity type nitride based compound semiconductor layer 31 a.Moreover, in case where the conductive carrier substrate 32 is made of ametal material having excellent electrical conductivity, the carriersubstrate 32 itself is usable as an electrode, which thus obviates aneed for forming the second electrode 34.

In this fashion, in a method for manufacturing a vertical nitride-basedsemiconductor light emitting device according to the invention, a GaNsubstrate is separated unharmed via wet-etching, instead of being groundand abraded via lapping or polishing. This allows recycling of thehigh-priced GaN substrate, thereby reducing production costs. Further, anitride-based compound semiconductor is grown on a high-quality GaNsubstrate by lateral growth. This produces a higher-qualitynitride-based compound semiconductor layer than the GaN substrate,thereby enhancing brightness of the light emitting device.

As set forth above, according to the invention, the expensive GaNsubstrate is separated without impairment via wet-etching, andconsequently recyclable. This advantageously lowers manufacture costsfor the nitride-based compound layer, GaN substrate and nitride-basedsemiconductor light emitting device. Also, the nitride-based compound ornitride-based compound semiconductor is laterally grown, advantageouslyproducing the nitride-based compound semiconductor, the GaN substrateand the nitride-based semiconductor light emitting device, which exhibita higher quality than the GaN substrate for growing such materials.Especially, the invention advantageously improves brightness of thenitride-based semiconductor light emitting device.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A method for fabricating a nitride-based compound layer, comprisingsteps of: preparing a GaN substrate; forming a mask layer with apredetermined pattern on the GaN substrate to expose a partial area ofthe GaN substrate; forming a buffer layer on the partially exposed GaNsubstrate, the buffer layer made of a material having a 10% or lesslattice mismatch with GaN; laterally growing a nitride-based compoundfrom a top surface of the buffer layer toward a top surface of the masklayer and vertically growing the nitride-based compound layer to apredetermined thickness; and removing the mask layer and the bufferlayer via wet-etching to separate the nitride-based compound layer fromthe GaN substrate.
 2. The method according to claim 1, wherein thebuffer layer has a 5 % or less lattice mismatch with GaN.
 3. The methodaccording to claim 1, wherein the buffer layer comprises one selectedfrom a group consisting of ZnO, Ga_(2 O) _(3 and ZrB) ₂.
 4. The methodaccording to claim 1, wherein the mask layer comprises a silicon oxidefilm or a silicon nitride film.
 5. The method according to claim 1,wherein a wet-etching solution used in the wet-etching comprises HCl orHF.
 6. A method for fabricating a GaN substrate comprising steps of:preparing a seed GaN substrate; forming a mask layer with apredetermined pattern on the seed GaN substrate to expose a partial areaof the GaN substrate; forming a buffer layer on the partially exposedseed GaN substrate, the buffer layer made of a material having a 10% orless lattice mismatch with GaN; laterally growing the GaN from a topsurface of the buffer layer toward a top surface of the mask layer andvertically growing the GaN to form the GaN substrate with apredetermined thickness; and removing the mask layer and the bufferlayer via wet-etching to separate the GaN substrate from the seed GaNsubstrate.
 7. The method according to claim 6, wherein the buffer layerhas a 5% or less lattice mismatch with GaN.
 8. The method according toclaim 6, wherein the buffer layer comprises ZnO, Ga₂O₃ and ZrB₂.
 9. Themethod according to claim 6, wherein the mask layer comprises a siliconoxide film or a silicon nitride film.
 10. The method according to claim6, wherein a wet-etching solution used in the wet-etching comprises HClor HF.
 11. The method according to 6, wherein the GaN substrate formingstep comprises growing the GaN by HVPE.
 12. A method for fabricating avertical nitride semiconductor light emitting device, comprising stepsof: preparing a GaN substrate; forming a mask layer with a predeterminedpattern to expose a partial area of the GaN substrate; forming a bufferlayer on the partially exposed GaN substrate, the buffer layer made of amaterial having a 10% or less lattice mismatch with GaN; laterallygrowing a first conductivity-type nitride-based compound semiconductordoped with first conductive impurities from a top surface of the bufferlayer toward a top surface of the mask layer and vertically growing thefirst conductivity-type nitride-based compound semiconductor to form afirst conductivity-type nitride-based compound semiconductor layer, andgrowing an active layer made of a nitride-based compound on the firstconductivity-type nitride-based compound semiconductor layer and asecond conductivity type nitride-based compound layer doped with secondconductive impurities on the active layer, thereby forming a lightemitting structure. forming a conductive carrier substrate on the lightemitting structure; and removing the mask layer and the buffer layer viawet-etching to separate the light emitting structure from the GaNsubstrate.
 13. The method according to claim 12, wherein the bufferlayer has a 5 % or less lattice mismatch with the GaN.
 14. The methodaccording to claim 12, wherein the buffer layer comprises one selectedfrom a group consisting of ZnO, Ga₂O₃ and ZrB₂.
 15. The method accordingto claim 12, wherein the mask layer comprises a silicon oxide film or asilicon nitride film.
 16. The method according to claim 12, wherein awet-etching solution used in the wet-etching comprises HCl or HF. 17.The method according to claim 12, wherein the light emitting structureforming step comprises growing the nitride-based semiconductor compoundby MOCVDE.
 18. The method according to claim 12, further comprisingforming a first electrode on an underside of the first conductivity-typenitride-based compound semiconductor layer from which the GaN substrateis separated, and a second electrode on a top surface of the conductivecarrier substrate.